The present invention relates to a producing method of an optical deflection device provided in an image exposure device used for an image forming apparatus such as a laser beam printer, laser copier, and laser facsimile device.
In the image forming apparatus such as the laser beam printer, the laser light is made incident on a rotary polygon mirror (polygon mirror) which is rotated at an equal speed, based on the read-out information as a writing means of the image, and the reflected light is made to scan and is projected on the photoreceptor surface and the image recording is conducted.
When the polygon mirror is rotated at the low speed, it is directly fixed on a rotation axis of a drive motor, but when it is rotated at the high speed, the rotary polygon mirror is fixed on the outer cylindrical member and is rotated by using an air dynamic pressure bearing (air bearing) which is rotated in the floating status without touching the fixedly arranged inner cylindrical member. Further, because the air dynamic pressure bearing is rotated in the non-contact status, there are features such as a long life and low noise.
For the optical deflection device having the dynamic pressure bearing, the present applicant discloses the technology by each specification of Tokkaihei No. 7-243437, 7-259849, 8-114219 and 8-121471. The present applicant further discloses Tokkai 2001-221972 in which the inner peripheral surface of a polygon mirror and the outer peripheral surface of an outer cylindrical bearing are adhered together, and a flange member is adhered to either the outer peripheral surface of the outer cylindrical bearing or an end portion of the polygon mirror.
In the optical deflection device having: a rotor unit including a rotary polygon mirror having a plurality of mirror surfaces on the side surface portion and a holding member holding the polygon mirror; an air dynamic pressure bearing including a rotary bearing member to rotatably support the rotor unit and a fixed bearing member; and a stator unit which supports the fixed bearing member, including a winding coil which is oppositely arranged to the magnet, in the conventional assembly process in which the outer peripheral surface of the rotary bearing member and the inner peripheral surface of the holding member are fixed by the shrink-fit, it is necessary to increase the fixing strength that the shrink-fit margin (that is, the difference between the outer diameter of the rotary bearing member and the inner diameter of the holding member) is increased.
However, when the shrink-fit margin is increased, the inner diameter of the rotary bearing member changes. Particularly, when a portion of the outer peripheral surface of the rotary bearing member and the inner peripheral surface of the holding member are shrunk-fit and fixed, the inside stress of the rotary bearing member becomes non-uniform, and the inner peripheral surface of the rotary bearing member is inclined surface-like, and the rotation becomes unstable. Further, in the non-uniformity of the inside stress of the rotary bearing member, the inner peripheral surface of the rotary bearing member is deformed due to the change of the environmental temperature, and the unstable rotation is generated.